Angular position determining systems using time scanned arrays

ABSTRACT

Disclosed are systems for determining the angular position of a target with respect to a reference location. One such system employs a novel array of antenna units at a reference location. The units of the array are coupled together by delay lines so that a pulse supplied to one of the units is in turn sequentially supplied to the remaining units, causing a pulse train to be radiated from the array. A target located in the field of the array is illuminated by a pulse train which has a phase distribution proportional to the angular position of the target with respect to the array and therefore with respect to the reference location. This phase distribution is detected by forming a predetermined electrical signal which can be used to provide an indication of the target&#39;&#39;s angular position either at the reference location alone, the target alone, or at both the reference location and the target.

United States Patent [191 Baurle et a1.

[ ANGULAR POSITION DETERMINING SYSTEMS USING TIME SCANNED ARRAYS [75]Inventors: Herbert F. Baurle; Raymond J. Masak, both of East Northport,

21 Appl. 1%.; 67,821

[52] US. Cl. 343/102, 343/16 R, 343/100 SA, 343/108 M [51] Int. Cl. G015l/02 [58] Field of Search... 343/100 SA, 106 D, 113 DE, 343/102, 108 M,16 R [56] References Cited UNITED STATES PATENTS 3.518.669 6/1970 Vogel343/l6 R 3,234,554 2/l966 Earp et al 343/108 M [451 Mar. 19, 1974Primary Examiner-Benjamin A. Borchelt Assistant ExaminerRichard E.Berger 5 ABSTRACT Disclosed are systems for determining the angularposition of a target with respect to a reference location. One suchsystem employs a novel array of antenna units at a reference location.The units of the array are coupled together by delay lines so that apulse supplied to one of the units is in turn sequentially supplied tothe remaining units, causing a pulse train to be radiated from thearray. A target located in the field of the array is illuminated by apulse train which has a phase distribution proportional to the angularposition of the target with respect to the array and therefore withrespect to the reference location. This phase distribution is detectedby forming a predetermined electrical signal which can be used toprovide an indication of the targets angular position either at thereference location alone, the target alone, or at both the referencelocation and the target.

19 Claims, 14 Drawing Figures i PULSE MEANS I SUPPLYING PATENTEDHAR 19m4 SHEEI 1 0F 5 FIG.

AMPLITUDE fFREQUENCY f0 TIME I UNIT I3 I I FIG 2 UNIT I4 I I I I I uNITI5 I I l 1 I I l UNIT l6 TIME I T I I AMPLITUDE F I G 3 PULSE TRAIN AsREcEIvED I I ON BROADSIDE PULSE TRAIN As RADIATED AMPLITUDE f I f iPULSE TRAIN U U H 4 0 AS REcEIvED OFF BROADSIDE l I I I I I I I I I I II PULSE TRAIN AS RADIATED FIG. 4b

PAIENIEBMAR 19 I974 3,798,645

sum a nr 5 AMPLITUDE 22 /4 2| UNIT I3 UNIT I4 I UNITI5 I 22 2| UNIT I6bTlME 1 1 T 1 1 FIG. 5

20 l3 l4 l5' l6 I I I 1 A fkj PULSE SUPPLYING I 9% I H MEANS 9 k 23 24I7 23 24 I8 23 24 I9 23 24 FIG. 6

PULSE SUPPLYING ARRAY RECEIVER MEANS FIG. 7

PAIENIEDIIIIII I 9 I974 3; 798x345 SHEET & UF 5 AMPLITUDE I l I l I I lI I I I I I +TIME I III I I I I I I FIG. 8

j ;37 PHASE FRONT DETEcTIoN OUTPUT END MEANs FIELD LocAL INTENSITYOSCILLATOR Z TIME 37 FIG. Io /3s 39 ;4O wIDE MATCHED I? OUTPUT BANDPASSFILTER FROM FILTER BANK o FRONT END F|G.|I

PATENTEU MR 1 9 I974 SHEET 5 BF 5 WIDE OUTPUT FOURIER BANDPASS FROMFILTER TRANSFORMER FRONT END FIG. I2

WIDE NARROW BANDPASS BANDPASS FREQUENCY FROM Fl LTER F 1 LTER DISC.FRONT 5'2 OUTPUT 44 RAMP VOLTAGE GENERATOR CONTROLLED OSCILLATOR DISABLEAMP LPF FIG. I3

ANGULAR POSITION DETERMINING SYSTEMS USING TIME SCANNED ARRAYS CROSSREFERENCE TO RELATED APPLICATIONS The present invention relates toangular position determining systems such as those described inapplicants simultaneously filed copending US. application, Ser. No.67,820, filed Aug. 28, 1970, entitled Angular Position DeterminingSystem Compensated For Doppler, which is assigned to the same assigneeas the present application.

BACKGROUND OF THE INVENTION This invention relates to novel angularposition determining systems utilizing a time scanned array toaccurately determine the position of targets located in the field of thearray.

Present angular position determining systems generally employ scanningbeams formed by variably phased arrays of rotating antennas, to obtainthe required positional information. There are several disadvantagesinherent in these systems, some of which are the low rate at whichangular position for a plurality of targets is obtained, the cost ofvariable phase shifters in the phased array system, and theunreliability of mechanically scanned antenna systems.

Angular position determining systems have previously been proposedutilizing time scanned arrays. A time scanned array is one in which apredetermined broad radiation pattern is formed in space, instead of themore conventional pencil type scanning beam. The angular position oftargets in the field of the time scanned array can be obtained from thenature of the radiation pattern at the position of the target, thereforeone advantage of this type of system is that it is capable of providinginformation for a plurality of targets simultaneously.

The time scanned array systems disclosed in the prior art in general andby C. W. Earp, in particular, have several disadvantages of which it isan object of applicants' invention to overcome.

Firstly, prior art time scanned arrays generally have employedmechanical switches to separately excite the individual units of thearray in an appropriate sequence. Such switches are expensive andunreliable as well as being extremely complex when large numbers ofantenna units are contained in the array. Furthermore, such switchesgreatly increase the power requirements of the overall system andpreclude use of the array for the purpose of signal reception.

Secondly, prior art systems have generally contemplated a continuouscyclical type of transmission and a receiver which averages theinformation obtained from such transmissions to provide the desiredangular information. This type of operation is therefore not effectivein an interlaced or intermittent mode since the receiver is dependentupon continuous transmissions.

Finally, and referring to C. W. Earps US. Pat. No. 3,234,554, inparticular, prior art time scanning systems are extremely susceptible tomultipath transmissions. This susceptibility is caused by severalinadequacies in these systems, two of which are the requirement for aseparate reference signal (the ground-reflected signal in the Earppatent) and the failure to incorporate any method for distinguishing thedesired information signals, received from the array, from multipathtransmissions caused by reflections.

In order to overcome these difficulties a novel time scanned array isdisclosed which does not utilize undesirable mechanical switching toexcite the units of the array. The system avoids many of theaforementioned prior art multipath problems since. no separate referencesignal is utilized in obtaining angular information and since in severalembodiments a special electrical beam type signal (describedhereinafter) is formed in the receiver, one of whose purposes is toenable undesired multipath transmissions to be rejected.

SUMMARY OF THE INVENTION Objects of the invention therefore are: toprovide a novel system capable of determining the angular position of atarget with respect to a reference location; to provide such a systemcapable of providing angular information to either the target, thereference location, or both, to provide such information at a high datarate; and to provide such a system capable of operating in a multipathenvironment.

Further objects of the invention are: to provide a novel time scannedarray antenna useful in such an angular position determining system, toprovide such an antenna utilizing fixed delay lines as couplingelements, to provide such an antenna capable of being easily zoomed to aparticular sector in space; and to provide such an antenna additionallyuseful as a reception antenna in an angular position determining system.

Still further objects of the invention are: to provide novel receiversuseful in such angular position determining systems, to provide suchreceivers capable of operating in a multipath environment, and toprovide a receiver capable of producing an output indication of theangular position of the target in real time.

In accordance with the invention, there is provided a system fordetermining the angular position of a target with respect to a referencelocation, which comprises an array of antenna units at the referencelocation; means for supplying a pulse type signal to a unit of thearray; delay means for coupling the pulse type signal to each of theremaining units of the array in a predetermined sequence and having apredetermined phase relationship such that each unit radiates acorresponding pulse type signal during a time interval unique to thatunit, whereby a target located in the field of the array is illuminatedby a train of radiated pulses having a phase distribution which isproportional to the angular position of the target in relation to thearray and means for receiving the train of radiated pulses which haveilluminated the target.

The system further includes means for detecting the phase distributionof the received pulse train, by forming an electrical signal having awaveshape substantially equivalent to the field intensity characteristicwhich would be formed at the target by a predetermined scanning beamilluminating the target, and for providing an output indication of theangular position of the target with respect to the array and thereforewith respect to the reference location.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an illustration of anembodiment of the invention incorporating a time scanned array antenna;

FIGS. 2, 3, 4a, 4b and 5 are graphical illustrations of pulse typesignals useful in understanding the embodiments of FIG. 1;

FIG. 6 is an alternate embodiment of an array antenna constructed inaccordance with the teachings of the invention;

FIG. 7 is an embodiment of the invention illustrated as an aircraftlanding system;

FIG. 8 is a graphical illustration useful in understanding theembodiment of FIG. 7;

FIG. 9 is a novel receiving apparatus useful in the sys tem of FIG. 7;

FIG. 10 is a graphical illustration useful in understanding theembodiment of FIG. 9, and

FIGS. 11, 12 and 13 are alternate phase detection means useful in theembodiment of FIG. 9.

DESCRIPTION AND OPERATION OF THE EMBODIMENTS OF FIGS. 1 AND 6 Referringto FIG. 1 there is shown an embodiment of applicants invention used asan aircraft landing system in which targets such as aircraft 10 and 11are illuminated by the radiations from the array antenna within dottedbox 12 which for purposes of this embodiment defines a referencelocation. It will be recognized that applicants invention is not limitedto landing systems but is useful wherever the angular position ofaplurality of targets (for example aircraft, boats. automobiles, etc.) isto be determined. Furthermore, reference location 12 need not bestationary as shown in the illustration but may for example be containedin an aircraft in which case a ground station may be used as a target.

Contained within reference location 12 is an array antenna consisting ofantenna units l3, 14, 15 and 16 coupled together by delay lines 17, 18and 19. These units may be any conventional radiating antenna elementssuch as dipoles or horns, and may consist of more than one element aswill be explained hereinafter. Also included in the reference locationis means 20 for supplying a pulse type signal to a unit 13 of the array.This means may be a conventional pulse transmitter or other pulsegeneration circuit and may supply either a single pulse or a group ofpulses. Means 20 need not be included in the reference location but maybe remote from it and the extent of the reference location in generalmay be expanded or contracted to take into account any area in which thearray is located and with respect to which angular position informationis desired.

The array shown contains four units l3, l4, l5 and 16 by way of exampleonly which units are shown for purposes of clarity to be larger withrespect to the distance to the targets than would be practical in actualsystems. Furthermore, practical systems would employ arrays havinglarger numbers of units, resulting in larger pulse trains, to obtainmore accurate angular position determination from the phase distributionof these pulse trains.

Referring now to FIG. 2, there is shown a typical pulse type signalsupplied to unit 13 by means 20 which consists of a single pulse ofcarrier signal at a carrier frequency f,, and having a predeterminedduration 1. Delay lines 17, 18 and 19, which comprise delay means forcoupling the supplied pulse type signal to each of the remaining unitsof the array in a predetermined sequence and with a predetermined phaserelationship such that each unit radiates a corresponding pulse typesignal during a time interval unique to that unit, are selected to havefixed predetermined delays which are equal to the duration t of thepulse of FIG. 1. It will be recognized that the fixed individual delaylines of FIG. 1 could be replaced by a single multitap delay line whichwould supply each unit of the array with the pulse of FIG. 2 in themanner described above. In this manner each unit of the array radiates acorresponding pulse during a unique time interval as shown in FIG. 3,which illustrates the time of arrival at each of the units of the array13, 14, 15 and 16 of the envelope of the pulse supplied to unit 13.

Targets such as aircraft in the field of the array are illuminated by aradiated pulse train (one pulse from each unit) rather than the singlepulse of FIG. 2 although the extent of the field of the array isdetermined by the radiation pattern of a single unit radiating alone,since each unit radiates independently of the other units and there isno contribution or interference from the radiation of other units in thearray as is the case with conventional scanning beam arrays.

The angular position of targets in the field of this array can bedetermined from the phase distribution of the pulse train (i.e.,progressive phase shift between pulses) sensed at each target becausetargets at different positions in space will sense different phasedistributions. The reason for this is clearly seen by referring back toFIG. 1 and looking at lines a a a a and b b b and b drawn betweencorrespondingly numbered units of the array and aircraft 10 and 11.These lines represent the distance traveled by the pulse radiated fromeach unit of the array to the targets 10 and 11. Since aircraft 10 isassumed to be on the broadside axis of the array (axis perpendicular tothe plane of the array) the a lines are approximately the same lengthindicating that it takes the same amount of time for the pulse from unit13 (line a to reach the target as it does for the pulse from unit 16(line a Therefore aircraft 10 will sense the pulse train substantiallyas it was transmitted or in other words having the same phasedistribution as that introduced by delay lines 17, 18 and 19. FIG. 4ashows a graph of the envelopes of the pulses as radiated from eachelement of the array and the pulse train sensed by an aircraft such as10, which is on the broadside axis of the array. Note that there issubstantially no phase shift between pulses of the pulse trainillustrated since it is assumed that no phase shift was introduced bydelay lines l7, l8 and 19.

On the other hand looking at lines b drawn to aircraft 11, it can beseen that the distance (line 11 between the aircraft and unit 13 is lessthan the distance between the aircraft and unit 14 (line b and likewisefor units 15 and 16. This means that it takes longer for the pulse fromunit 16 to arrive at aircraft 11 than it does for the pulse from unit 15and so on for units 14 and 13. This introduces a phase shift between thepulses of the pulse train, as sensed at the aircraft 11, which causesthe phase distribution of the pulse train to differ from that sensed bythe aircraft 10 on the boresight axis of the array. This change in phasedistribution is proportional to the difference in path length betweenunits of the array and the aircraft 1 1, which in turn is proportionalto the angular position of the aircraft with respect to the array (byconventional trigonometry). Therefore, the angular position of theaircraft can be determined by measuring this phase distribution withnovel receiving apparatus herein described. FIG. 4b shows therelationship between the pulse train transmitted from the array and thepulse train sensed by aircraft 1 l and shows the small phase shiftbetween pulses of the pulse train sensed at the target caused by theangular position of the target.

In the embodiment illustrated the phase shift between pulses radiated bythe array and therefore the phase shift between pulses on the broadsideaxis of the array is assumed to be zero. If desired an original phaseshift between pulses can be introduced before radiation by the array,thereby establishing a new reference phase distribution on the broadsideaxis of the array with respect to which the angular position of targetsnot located on the broadside axis can be measured.

The overall pulse train sensed by aircraft 11 will not only have a phasedistribution which differs from the reference phase distribution sensedby aircraft on the broadside axis, but will also have a carrierfrequency which correspondingly differs from that sensed by target 10.Several embodiments of the receiving apparatus disclosed herein areadapted to detect this change in carrier frequency and to provide anoutput indication of the targets angular position based on it.

The embodiment of FIG. 1 shows a linear array by way of example only,and if desired other array forms can be assembled to provide coverageover larger sectors of space in a manner well known in the art.Furthermore, both azimuth angle and elevation angle information can beobtained by suitable positioning of a pair of array antennas andoperating them in an interlaced mode. For example a first linear arraypositioned horizontally with respect to the ground could be utilized toobtain azimuth angle information and a second linear array positionedvertically with respect to the ground could be utilized to obtainelevation angle information for targets such as aircraft located in thefield of these arrays.

The use of delay lines l7, l8 and 19 for coupling a pulse type signal toeach unit of the array of FIG. 1 provides several distinct advantagesover prior art systems, one of which is made apparent by assuming thatmeans 20 supplies not a single pulse, as in FIG. 2, but a pair of likepulses having a spacing (i.e. between leading edges of the pulses)selected to be equal to the width t of the pulse, and therefore equal tothe delay of delay lines l7, l8 and 19. In the embodiment of FIG. 1,when a single pulse is supplied to the array, the field of the array isdetermined by the radiation pattern of a single unit radiating alone.However, when a pair of pulses are supplied to the array, at the timewhen the first pulse excites unit 14, the second pulse will excite unit13 and the corresponding radiation pattern from each unit will combineto restrict somewhat the field of the array. As a result, when all theunits of the array are excited in this manner (i.e. sequentially inpairs) the field of array is restricted, or zoomed, to approximatelyone-half of its original field.

FIG. 5 is a graphical illustration showing the time of arrival of theenvelopes of a pair of pulses 21 and 22 supplied by means 20 to theradiating units of the array of FIG. 1. The illustration clearly showsthe overlap between pulse 21 and pulse 22 as they arrive at differentunits of the array. This overlap results in the aforementionedrestriction of the field of array and thereby achieves a course zoomingof the array to a narrower sector in space, simply and inexpensively,without changing the physical position of the array or its angularposition determining characteristics.

An alternate method of obtaining the same result (array fieldrestriction) would be to construct an array such as that shown in theembodiment of FIG. 6 which comprises antenna units l3, l4, l5 and 16connected together with delay lines l7, l8 and 19 as in the array ofFIG. 1, but in this case each antenna unit consists of two radiatingelements 23 and 24 spaced at a suitable antenna unit spacing (preferablyone-half wavelength). Only one pulse need be supplied to unit 13 of thearray by means 20 since the overlapping radiation patterns will resultfrom the simultaneously excited elements 23 and 24, in each unitproducing the same restriction in the field of the array as describedabove. If greater restrictions in the field of the array, for example,of one-third, one-fourth or more, is desired, it can be accomplished bysupplying a third, fourth or more pulses in the embodiment of FIG. 1 orby including a third, fourth or more elements in the embodiment of FIG.6, or by combining the two embodiments and supplying two or more pulsesto the array in the embodiment of FIG. 6.

DESCRIPTION AND OPERATION OF THE SYSTEM OF FIG. 7

Since the overall radiation pattern transmitted from the array of FIG.1, for example, is a broad one, a plurality of targets in the field ofthe array can obtain the desired angular position informationsimultaneously. Referring now to FIG. 7 which shows two such targets 25and 26 in the field of an array 27, assumed to be similar to, that ofFIG. 1, located at a reference location 28. Both targets include a novelreceiving apparatus 29, described hereinafter, so that upon entering thefield of the array they can obtain an indication of their angularposition with respect to the reference location. In the embodiment ofFIG. 7 the reference location also includes a novel receiving apparatus30 in order to provide at the reference location an indication of theangular position of the aircraft. For this information to be obtained,the pulse train radiated by the array is either reflected or receivedand retransmitted by the aircraft to the reference location, but ineither case the phase distribution sensed by the aircraft is preservedso that it can be measured in receiving apparatus 30.

A further advantage of including a receiving apparatus at the referencelocation is that both range and angular information for an aircraft canbe obtained from each transmission of a pulse train by the array sincethe range is represented by the round trip travel time of the pulsetrain from the array to the target and back to the receiving apparatus,and the angular information is contained in the phase distribution ofthe received pulse train.

While receiving apparatus 29 in the aircraft 25 and 26 both includeconventional omnidirectional antennas 31 for receiving the pulse trainfrom the array, the receiving apparatus 30 located at the referencelocation 28 is shown as connected to the original array 27. This featureis particularly advantageous since the use of delay lines in the arrayinsures that there will be antenna gain. The received pulse train whicharrives at each unit of the array is combined through the delay lines ofthe array to provide at the input of the receiver 30 a pulse trainhaving a staircase amplitude function similar to that shown in FIG. 8(which shows the envelope of such pulse train for a target on thebroadside axis). While this envelope alone could be used to provide anindication of angular position (by detecting its slope) the receivingapparatus 30 described herein are adapted to detect the phasedistribution of the pulses of the carrier frequency under the envelope(not shown), as this is a more accurate form of detection and thereforemore useful in angular position determining systems such as aircraftlanding systems where accuracy is required.

Another particularly useful characteristic of the system of FIG. 7 isthe ability to transmit and receive selected other information, forexample IFF, by additionally coding the pulse supplied by pulsegenerator 20 to be representative of this other information. The codingcan be of any suitable kind well known in the art, for example linear FMphase coding. This coding can be adapted so as not to disturb theangular position determination since in that case what is measured isthe phase distribution of the overall pulse train and not the phasecharacteristics of individual pulses. Receiving apparatus used in such asystem may incorporate any conventional decoding scheme suitable for thetype of coding utilized, thereby providing additional information to theaircraft or the reference location for a single pulse traintransmission.

DESCRIPTION AND OPERATION OF THE EMBODIMENT OF FIG. 9

Turning now to a novel receiving apparatus useful in a system fordetermining the angular position of targets with respect to thereference location, FIG. 9 shows a block diagram of an embodiment builtin accordance with one aspect of the invention.

Shown in dotted box 33 of FIG. 9 are means for receiving the train ofradiated pulses which have illuminated the target. This means is shownas a conventional omnidirectional antenna 34 in combination with thereceiver front end 35 and a local oscillator 36, which combinationprovides a pulse train at the input to a phase detection means 37. Shownas block 37 is means for detecting the phase distribution of thereceived pulse train, and for providing an output indication of theangular position of the target with respect to the array.

In certain prior art angular position determining systems a pencil typescanning beam scans through a sector of space illuminating a target fora short instant of time and then proceeding on through the sector. Atthe target a plot of field intensity vs. time would be similar to thatshown in FIG. 10 as the pencil beam sweeps across the target. Aspreviously stated one of the advantages of the present invention is thatno such variation in field intensity is produced since all targets inthe field of the array are illuminated at substantially the same time bythe broad radiation pattern of the array. However, in accordance withthe present invention resolution capability identical to that of thescanning beam system can be obtained by forming in the receiver anelectrial signal whose waveshape is the equivalent of the fieldintensity characteristic (an example of which is shown in FIG. 10) whichwould have been formed at a target by a scanning beam illuminating thetarget. This electrical signal (herein called beam type signal) onceformed in the receiver helps discriminate against multipathtransmissions since the particular field intensity plot of FIG. 10 andtherefore its equivalent electrical signal can be easily identified inthe receiver and locked in during target tracking, thereby preventingmultipath transmissions from interfering. In addition, formation of thissignal allows the receiver herein described to determine the angularposition of targets from a single transmission of the aforementionedpulse train, thereby permitting the entire system to operate inintermittent modes.

The different embodiments of phase detection means 37 incorporating thistechnique (beam type signal forming) are shown in FIGS. 11, 12 and 113.The receivers disclosed do not incorporate an undesirable referencesignal as do the prior art systems since all phase distributionmeasurements takes place directly on the received pulse train. Prior artsystems use the reference signal as a frequency standard for comparisonpurposes in angular position determination and therefore are subject tothe inherent multipath problems caused by this reference signal.

Referring to FIG. 11, one embodiment of phase detection means 37 isshown as comprising a plurality (i.e. bank) of matched filters 38 whichmay, for example, consist of a multitap delay line and a phase matrix.The received pulse train is fed to the filters 38 from front end 35through wide bandpass filter 40 which is centered approximately aboutthe carrier frequency to eliminate extraneous noise. Since each matchedfilter is adapted to add the pulses of the pulse train and produce anoutput signal for a pulse train having a particular phase distribution,only the filter matched to the phase distribution sensed by the targetwill provide an output signal on the corresponding one of the terminals39. Since this output signal is formed in much the same way that aphased array antenna forms a scanning beam in space, (pulses combinedaccording to their phase to produce a maximum contribution), the outputsignal will appear on an appropriate one of the terminals 39 as theaforementioned beam type signal. This signal (output indication)represents the angular position of the target with respect to the arraywith different angular positions represented by different phasedistributions providing an output signal on different ones of theterminals 39.

Referring now to FIG. 12 a second embodiment of phase detection means 37is shown which employs a wide bandpass filter 410 centered approximatelyabout the carrier frequency to eliminate extraneous noise. Furtherincluded is a Fourier transformer 41 which, as is well known to the art,has the ability to accept an input signal and to provide an outputindication in real time which represents the mathematical Fouriertransform of the input signal. In effect the Fourier transformerperforms a spectrum analysis on the input signal and therefore theoutput indication, which in this case is a pulse in real time, isrepresentative of the frequency of the overall received pulse trainwhich in turn is representative of the angular position of the target asdescribed previously. Since the output indication is provided in realtime it is more easily utilized for display purposes than was theprevious indication.

A third embodiment of phase detection means 37 useful in a receiverbuilt in accordance with the invention is shown in FIG. 13. Thisembodiment provides several advantages over the previous ones in thatthe entire detection process takes place in the frequency domain,thereby providing relatively accurate position determination over acontinuous period of time. Phase detection means 37 in FIG. 13 is shownas comprising a wide bandpass filter 40 centered approximately about thecarrier frequency which as in previous cases, accepts the pulse trainfrom front end 35 and filters out extraneous noise. Further included isa mixer 42 which is supplied with a signal from voltage controlledoscillator 44 as well as the pulse train from bandpass filter 40. Priorto receiving any pulse trains a ramp generator 43 supplies a ramp signalto the voltage controlled oscillator in order to cause the frequency ofthe oscillator to vary from zero to a frequency equal to the bandwidthof bandpass filter 40. This is done in order to match the frequency ofany possible received pulse trains to the characteristic defined bynarrow bandpass filter 45 since the pulse train supplied from bandpassfilter 40 may not be centered about the same frequency as narrowbandpass filter 45. The frequency vs. amplitude characteristic ofbandpass filter 45 is matched to the waveshape of the signal which wouldbe created if the pulses of a received pulse train were combined to formthe aforementioned beam type signal. Therefore if received signals donot combine in filter 45 to match the characteristic of the filter theyare rejected and no output indication is provided. Upon reception of aproper signal (i.e. a pulse train that matches the characteristic offilter 45) frequency discriminator 46 in combination with low passfilter 47 generates a control voltage which is representative of thecenter frequency of the received signal. This control voltage is appliedthrough amplifier 48 to the control input of oscillator 44 and to rampgenerator 43, disabling the ramp generator. In effect this locks thereceived signal into the characteristic of bandpass filter 45, sinceshould the target change in angle, causing a change in frequency of thereceived pulse train, the change would be sensed by discriminator 46 andthe frequency of oscillation of oscillator 44 would be changed throughthe feedback loop to compensate for the change in target angle. Anoutput indication which is representative of the targets angularposition can be taken from the output of oscillator 44, since the signalfrequency at this point necessarily varies with changes in frequency ofthe received pulse trains, which changes represent changes in phasedistribution and therefore changes in angular position. It should benoted that once bandpass filter 45 receives a signal which is matched tothis characteristic and the remainder of the feedback loop locks in, nomultipath signals can interfere with the tracking process generated inthe loop.

This type of frequency discrimination is particularly advantageous incombination with a time scanned array system, since once a target ispresent in the field of the array it receives continuous angularposition information, substantially immune from multipath interferencedue to reflection of the original transmission.

While there have been described what are at present considered to be thepreferred embodiments of this invention, it will be obvious to thoseskilled in the art that various changes and modifications may be madetherein without departing from the invention.

What is claimed is:

1. System for determining the angular position of a target with respectto a reference location, comprising:

an array of antenna units at said reference location;

means for supplying a pulse type signal to a unit of said array;

delay means for coupling said pulse type signal to each of the remainingunits of said array in a predetermined sequence and having apredetermined phase relationship such that each unit radiates acorresponding pulse type signal during a time interval unique to thatunit, whereby a target located in the field of said array is illuminatedby a train of radiated pulses having a phase distribution which isproportional to the angular position of said target in relation to saidarray;

means for receiving the train of radiated pulses which have illuminatedsaid target;

and means for detecting the phase distribution of said received pulsetrain, by forming an electrical signal having a waveshape substantiallyequivalent to the field intensity characteristic which would be formedat said target by a predetermined scanning beam illuminating saidtarget, and for providing an output indication of the angular positionof said target with respect to said array and therefore with respect tosaid reference location.

2. A system in accordance with claim 1, wherein said receiving anddetecting means are at said reference location and wherein said targetincludes means for receiving and retransmitting said radiated pulsetrain to said reference location, thereby providing said outputindication at said reference location.

3. A system in accordance with claim 1, wherein said receiving anddetecting means are at said reference location and wherein said radiatedpulse train is reflected by said target to said reference location,thereby providing said output indication at said reference location.

4. A system in accordance with claim 1, wherein said detecting meanscomprises a plurality of matched filters each matched to the phasedistribution due to a selected angular position thereby providing saidelectrical signal from the particular filter matched to the phasedistribution which corresponds to the angular position of said targetwith respect to said reference location.

S. A system in accordance with claim 1, wherein said receiving means andsaid detecting means are at said target thereby providing said targetwith an indication of its angular position with respect to saidreference location.

6. A system in accordance with claim 4, additionally capable oftransmitting and receiving selected other information;

wherein said pulse type signal supplying means comprises means forsupplying a pulse type signal coded to represent said other information;

and wherein there is additionally included at said target means fordecoding said received pulses and for providing a second outputindication representative of said other information.

7. System for determining the angular position of a target with respectto a reference location, comprising:

an array of antenna units at said reference location;

means for supplying a pulse type signal to a unit of said array;

delay means for coupling said pulse type signal to each of the remainingunits of said array in a predetermined sequence and having apredetermined phase relationship such that each unit radiates acorresponding pulse type signal during a time interval unique to thatunit, whereby a target located in the field of said array is illuminatedby a train of radiated pulses having a phase distribution which isproportional to the angular position of said target in relation to saidarray;

means for receiving the train of radiated pulses which have illuminatedsaid target;

and a Fourier transformer for detecting the phase distribution of saidreceived pulse train, by forming an electrical signal having a waveshapesubstantially equivalent to the field intensity characteristic whichwould be formed at said target by a predetermined scanning beamilluminating said target, and for providing an output indication in realtime which is representative of the angular position of said target withrespect to said array and therefore with respect to said referencelocation.

8. A landing system for determining the angular position of an aircraftwith respect to a reference location, comprising:

an array of antenna units at said reference location;

means for supplying a pulse type signal to a unit of said array;

delay means for coupling said pulse type signal to each of the remainingunits of said array in a predetermined sequence and having apredetermined phase relationship such that each unit radiates acorresponding pulse type signal during a time interval unique to thatunit, whereby an aircraft located in the field of said array isilluminated by a train of radiated pulses having a phase distributionwhich is proportional to the angular position of said target in relationto said array;

means for receiving the train of radiated pulses which have illuminatedsaid aircraft;

and means including a frequency lock loop for combining the pulses ofsaid received pulse train to form an electrical signal having awaveshape substantially equivalent to the field intensity characteristicwhich would be formed at said aircraft by a predetermined scanning beamilluminating said aircraft, the center frequency of said electricalsignal being representative of the angular position of said aircraftwith respect to said array and therefore with respect to said referencelocation.

9. Apparatus usable in a system for determining the angular position ofa target with respect to a reference location comprising:

an array of antenna units at said reference location;

means for supplying a pulse type signal to a unit of said array;

and delay means for coupling said pulse type signal to each of theremaining units of said array in a predetermined sequence and having apredetermined phase relationship such that each unit radiates acorresponding pulse type signal during a time interval unique to thatunit and such that all units of said array do not radiatesimultaneously, whereby a target located in the field of said array isilluminated by a train of radiated pulses having a phase distributionwhich is proportional to the angular position of said target in relationto said array,

10. Apparatus in accordance with claim 9, wherein each unit of saidarray comprises a single antenna element and wherein said supplied pulsetype signal comprises a single predetermined pulse thereby producingfrom said array a series of radiation patterns each corresponding to theradiation pattern produced by a single antenna element.

11. Apparatus in accordance with claim 9, wherein each unit of saidarray comprises a single antenna element and wherein said supplied pulsetype signal comprises a plurality of pulses having a predetermined widthand spacing thereby producing from said array a series of radiationpatterns each corresponding to the radiation pattern produced when anumber of said antenna elements, equal to the number of pulses supplied,simultaneously radiate a single pulse.

12. Apparatus in accordance with claim 9, wherein each antenna unitcomprises a plurality of antenna elements thereby providing from saidarray a series of radiation patterns each corresponding to the radiationpattern produced by a number of said antenna units, equal to the numberof pulses supplied in said pulse type signal, simultaneously radiating asingle pulse.

13. Apparatus in accordance with claim 9, wherein said array is a lineararray and wherein said delay means comprises fixed delay lines connectedbetween units of said array.

14!. Apparatus in accordance with claim 9, additionally capable oftransmitting selected other information wherein said pulse supplyingmeans comprises means for supplying a pulse type signal coded torepresent said other information.

15. Apparatus usable in a system for determining the angular position ofa target with respect to a reference location, wherein said target isilluminated by a train of radiated pulses having a phase distributionwhich is proportional to the angular position of said target withrespect to said reference location comprising:

means for receiving the train of radiated pulses which have illuminatedsaid target;

and means for detecting the phase distribution of said received pulsetrain, by forming an electrical signal having a waveshape substantiallyequivalent to the field intensity characteristic which would be formedat said target by a predetermined scanning beam illuminating saidtarget, and for providing an output indication of the angular positionof said target with respect to said array and therefore with respect tosaid reference location.

16. Apparatus in accordance with claim 15, wherein said receiving meanscomprises:

an array of antenna units;

and delay means for coupling said units together in a predeterminedsequence such that said pulses, when received by said antenna units, areassembled into a train of pulses having a staircase function waveform,said staircase function pulse train being representative of said phasedistribution.

17. Apparatus in accordance with claim 15, wherein said detecting meanscomprises a plurality of matched filters each matched to the phasedistribution due to a selected angular position thereby providing saidelectrical signal from the particular filter matched to the phasedistribution which corresponds to the angular position of said targetwith respect to said reference location.

and means, including a frequency locked loop, for I combining the pulsesof said received pulse train to form an electrical signal having awaveshape substantially equivalent to the field intensity characteristicwhich would have been formed at said target by a predetermined scanningbeam illuminating said target, the center frequency of said electricalsignal being representative of the angular position of said target withrespect to said array and therefore with respect to said referencelocation.

1. System for determining the angular position of a target with respect to a reference location, comprising: an array of antenna units at said reference location; means for supplying a pulse type signal to a unit of said array; delay means for coupling said pulse type signal to each of the remaining units of said array in a predetermined sequence and having a predetermined phase relationship such that each unit radiates a corresponding pulse type signal during a time interval unique to that unit, whereby a target located in the field of said array is illuminated by a train of radiated pulses having a phase distribution which is proportional to the angular position of said target in relation to said array; means for receiving the train of radiated pulses which have illuminated said target; and means for detecting the phase distribution of said received pulse train, by forming an electrical signal having a waveshape substantially equivalent to the field intensity characteristic which would be formed at said target by a predetermined scanning beam illuminating said target, and for providing an output indication of the angular position of said target with respect to said array and therefore with respect to said reference location.
 2. A system in accordance with claim 1, wherein said receiving and detecting means are at said reference location and wherein said target includes means for receiving and retransmitting said radiated pulse train to said reference location, thereby providing said output indication at said reference location.
 3. A system in accordance with claim 1, wherein said receiving and detecting means are at said reference location and wherein said radiated pulse train is reflected by said target to said reference location, thereby providing said output indication at said reference location.
 4. A system in accordance with claim 1, wherein said detecting means comprises a plurality of matched filters each matched to the phase distribution due to a selected angular position thereby providing said electrical signal from the particular filter matched to the phase distribution which corresponds to the angular position of said target with respect to said reference location.
 5. A system in accordance with claim 1, wherein said receiving means and said detecting means are at said target thereby providing said target with an indication of its angular position with respect to said reference location.
 6. A system in accordance with claim 4, additionally capable of transmitting and receiving selected other information; wherein said pulse type signal supplying means comprises means for supplying a pulse type signal coded to represent said other information; and wherein there is additionally included at said target means for decoding said received pulses and for providing a second output indication representative of said other information.
 7. System for determining the angular position of a target with respect to a reference location, comprising: an array of antenna units at said reference location; means for supplying a pulse type signal to a unit of said array; delay means for coupling said pulse type signal to each of the remaining units of said array in a predetermined sequence and having a predetermined phase relationship such that each unit radiates a corresponding pulse type signal during a time interval unique to that unit, whereby a target located in the field of said array is illuminated by a train of radiated pulses having a phase distribution which is proportional to the angular position of said target in relation to said array; means for receiving the train of radiated pulses which have illuminated said target; and a Fourier transformer for Detecting the phase distribution of said received pulse train, by forming an electrical signal having a waveshape substantially equivalent to the field intensity characteristic which would be formed at said target by a predetermined scanning beam illuminating said target, and for providing an output indication in real time which is representative of the angular position of said target with respect to said array and therefore with respect to said reference location.
 8. A landing system for determining the angular position of an aircraft with respect to a reference location, comprising: an array of antenna units at said reference location; means for supplying a pulse type signal to a unit of said array; delay means for coupling said pulse type signal to each of the remaining units of said array in a predetermined sequence and having a predetermined phase relationship such that each unit radiates a corresponding pulse type signal during a time interval unique to that unit, whereby an aircraft located in the field of said array is illuminated by a train of radiated pulses having a phase distribution which is proportional to the angular position of said target in relation to said array; means for receiving the train of radiated pulses which have illuminated said aircraft; and means including a frequency lock loop for combining the pulses of said received pulse train to form an electrical signal having a waveshape substantially equivalent to the field intensity characteristic which would be formed at said aircraft by a predetermined scanning beam illuminating said aircraft, the center frequency of said electrical signal being representative of the angular position of said aircraft with respect to said array and therefore with respect to said reference location.
 9. Apparatus usable in a system for determining the angular position of a target with respect to a reference location comprising: an array of antenna units at said reference location; means for supplying a pulse type signal to a unit of said array; and delay means for coupling said pulse type signal to each of the remaining units of said array in a predetermined sequence and having a predetermined phase relationship such that each unit radiates a corresponding pulse type signal during a time interval unique to that unit and such that all units of said array do not radiate simultaneously, whereby a target located in the field of said array is illuminated by a train of radiated pulses having a phase distribution which is proportional to the angular position of said target in relation to said array.
 10. Apparatus in accordance with claim 9, wherein each unit of said array comprises a single antenna element and wherein said supplied pulse type signal comprises a single predetermined pulse thereby producing from said array a series of radiation patterns each corresponding to the radiation pattern produced by a single antenna element.
 11. Apparatus in accordance with claim 9, wherein each unit of said array comprises a single antenna element and wherein said supplied pulse type signal comprises a plurality of pulses having a predetermined width and spacing thereby producing from said array a series of radiation patterns each corresponding to the radiation pattern produced when a number of said antenna elements, equal to the number of pulses supplied, simultaneously radiate a single pulse.
 12. Apparatus in accordance with claim 9, wherein each antenna unit comprises a plurality of antenna elements thereby providing from said array a series of radiation patterns each corresponding to the radiation pattern produced by a number of said antenna units, equal to the number of pulses supplied in said pulse type signal, simultaneously radiating a single pulse.
 13. Apparatus in accordance with claim 9, wherein said array is a linear array and wherein said delay means comprises fixed delay lines connected between units of said array.
 14. Apparatus in accordance with claim 9, additionally capable of transmitting selected other information wherein said pulse supplying means comprises means for supplying a pulse type signal coded to represent said other information.
 15. Apparatus usable in a system for determining the angular position of a target with respect to a reference location, wherein said target is illuminated by a train of radiated pulses having a phase distribution which is proportional to the angular position of said target with respect to said reference location comprising: means for receiving the train of radiated pulses which have illuminated said target; and means for detecting the phase distribution of said received pulse train, by forming an electrical signal having a waveshape substantially equivalent to the field intensity characteristic which would be formed at said target by a predetermined scanning beam illuminating said target, and for providing an output indication of the angular position of said target with respect to said array and therefore with respect to said reference location.
 16. Apparatus in accordance with claim 15, wherein said receiving means comprises: an array of antenna units; and delay means for coupling said units together in a predetermined sequence such that said pulses, when received by said antenna units, are assembled into a train of pulses having a staircase function waveform, said staircase function pulse train being representative of said phase distribution.
 17. Apparatus in accordance with claim 15, wherein said detecting means comprises a plurality of matched filters each matched to the phase distribution due to a selected angular position thereby providing said electrical signal from the particular filter matched to the phase distribution which corresponds to the angular position of said target with respect to said reference location.
 18. Apparatus in accordance with claim 15, wherein said detecting means comprises a Fourier transformer for developing said electrical signal and for providing said output indication in real time.
 19. Apparatus usable in a system for determining the angular position of a target with respect to a reference location, wherein said target is illuminated by a train of radiated pulses having a phase distribution which is proportional to the angular position of said target with respect to said reference location comprising: means for receiving the train of radiated pulses which have illuminated said target; and means, including a frequency locked loop, for combining the pulses of said received pulse train to form an electrical signal having a waveshape substantially equivalent to the field intensity characteristic which would have been formed at said target by a predetermined scanning beam illuminating said target, the center frequency of said electrical signal being representative of the angular position of said target with respect to said array and therefore with respect to said reference location. 